configure.ac: use pkg-config to find id3tag

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

diff -durN madplay-0.15.2b-orig/configure.ac madplay-0.15.2b/configure.ac
--- madplay-0.15.2b-orig/configure.ac	2019-02-14 21:34:01.507212449 +0100
+++ madplay-0.15.2b/configure.ac	2019-02-15 23:24:00.079876087 +0100
@@ -182,12 +182,13 @@
 *** environment variable to specify its installed location, e.g. -L<dir>.])
 ])
 
-AC_CHECK_LIB(id3tag, id3_tag_parse, :, [
+PKG_CHECK_MODULES(ID3TAG, id3tag, [
+	CFLAGS="$CFLAGS $ID3TAG_CFLAGS" LIBS="$LIBS $ID3TAG_LIBS"], [
 	AC_MSG_ERROR([libid3tag was not found
 *** You must first install libid3tag before you can build this package.
 *** If libid3tag is already installed, you may need to use the LDFLAGS
 *** environment variable to specify its installed location, e.g. -L<dir>.])
-], [-lz])
+])
 
 AC_FUNC_VPRINTF
 AC_CHECK_FUNCS(madvise localeconv)